1. Field of the Invention
The present invention relates to a pouring spout structure for a paper carton, a paper carton having the pouring spout, and a method of manufacturing such a pouring spout.
2. Background Art
Recently, paper cartons of small volume have been widely used in the field of beverages such as fruit juice, coffee, soup, and fermented lactic-drink, because they are handy and can be easily disposed of after their use is finished. Some of these paper cartons have a pouring hole sealed with a tab tape to be torn off to open the carton. For the paper carton of the type described, various studies have been made in order to prevent the contents of the carton from entering into the inner peripheral surface defining a pouring hole, or a pouring spout. An example is disclosed in U.S. Pat. No. 4,595,116 of which structure is illustrated in FIG. 16. According to this art, the pouring spout 1 has a laminate base material 2 (a paper-based laminate). A hole 3 is formed in the laminate base material 2 by means of punching it to make a hole of a predetermined shape. Thermoplastic resin or the like is then laminated on one surface 4 facing outside the carton of the laminate base material 2 and the other surface 5 facing inside the carton to form an outer waterproof layer 6 and an inner waterproof layer 7, respectively. A pouring spout 9 is provided at an attached portion 8 where the waterproof layers 6 and 7 are attached to each other inside the above mentioned pouring hole. A tab tape 10 is removably attached to the outer waterproof layer 6 to cover the pouring spout 9.
Laminate materials, which form the main body of the carton with the waterproof layers provided on the outer and inner surfaces of the above mentioned laminate base material, have a laminated layer structure of selected synthetic resin or metal foil. The selection and combination of these materials permit the paper carton to have desired properties such as waterproof properties, water resistance, shading, and gas barrier properties.
However, in such a structure with the waterproof layers attached to each other in the pouring hole and a pouring spout to be covered with the tab tape, both waterproof layers attached by lamination cover the inner peripheral surface defining the pouring hole. Accordingly, a pinhole or a thinner portion of the layer may be formed depending on the status of the inner peripheral surface defining the pouring hole at the time of heat-sealing of the synthetic resins of the inner and outer waterproof layers. This often results in a faulty seal in the inner peripheral surface defining the hole and permits the contents of the carton to enter into the inner peripheral surface through a gap formed at the attached portion. In order to obtain the gas barrier properties around the pouring hole having no laminate base material laminated thereon, a laminate film may be made by an aluminum foil and an oriented polyester film used as the components of the above mentioned inner and outer waterproof layers, considering the gas barrier properties and strength of the film. However, these components typically have poor heat sealing characteristics relative to each other, so that the thermoplastic resin must be laminated on the above mentioned laminate film, which complicates the layer structure of the whole laminate film and raises the cost. Though the sealing properties may be improved by providing higher sealing strength, an excessively high sealing strength may cause the tab tape to be torn off along with the outer waterproof layer. As a result, the pouring spout may be whitened upon tearing off the tab tape. In addition, only the poor waterproof properties can be obtained.
The above mentioned problem can be solved with lower sealing strength. The lower sealing strength may, however, cause problems of the leaking of the contents or poor preservation properties.
With respect to the above problems, the present invention is directed to simplify the structure of the pouring spout using a partial covering film to cover the inner peripheral surface defining the hole of the laminate base material, and an object of the present invention is to easily obtain such a pouring spout that no contents enter into the inner peripheral surface defining the hole.